Well, I'm asking specifically if the author saw corruption that snuck past the checksumming features that postgres has.
Extra layers are always good, but since I was one of the main authors of checksums in Postgres, I'd like to know if there's room for improvement. (Aside: the page checksum is only 16 bits, so if you have frequent corruption it's entirely believeable that a few sneak past. But I haven't seen it personally.)
If you care about your data: Use ECC, and use a checksumming filesystem like ZFS, and also on top of this all, export your WALs to a second machine.